docs: roadmap for designer-friendly install paths

Captures two install upgrades in dependency order so a future session can
pick them up without re-thinking:

  Tier 1 — scripts/setup.sh: one-liner installer for terminal-comfortable
  designers. Auto-generates JWT_SECRET, prompts for admin email/password,
  brings up docker compose, opens the browser. Floor: Docker Desktop must
  be installed (script exits with a friendly install link if not).

  Tier 2 — native installer: .dmg / .exe with no Docker, no terminal.
  Replaces MinIO with a local-filesystem storage adapter, bundles the
  Node backend + frontend dist into a single binary via pkg, wraps in a
  Tauri tray app. Designer double-clicks, gets a menu-bar icon, clicks
  "Open RefBoard."

Both unchecked in README roadmap and detailed in docs/install-roadmap.md
with file layout, estimated effort, and open questions.

README.md

@@ -289,6 +289,8 @@ See [CHANGELOG.md](CHANGELOG.md) for the version history (v0.1.0 → v0.5.0).
 
 - [x] Admin dashboard frontend (live at `/admin` — user create / reset-password / role / deactivate)
 - [x] Per-board activity log (uploads, board events, threads, comments — live via Socket.IO)
+- [ ] **One-click `setup.sh` installer** for designers — see [`docs/install-roadmap.md`](docs/install-roadmap.md)
+- [ ] **Native installer** (`.dmg` / `.exe`) with no Docker dependency — see [`docs/install-roadmap.md`](docs/install-roadmap.md)
 - [ ] Mobile-friendly read-only board view
 - [ ] Export board → PDF / image grid
 - [ ] Optional remote storage adapters (S3 direct, R2)